const fs = require('fs');
/*
fs.readFile('1.txt',(err,result1)=>{
    console.log(result1);
    fs.readFile('2.txt',(err,result2)=>{
        console.log(result2);
        fs.readFile('3.txt',(err,result3)=>{
            console.log(result3);
        })
    })
})*/
function p1(){
    return new Promise((resolve,reject)=>{
        fs.readFile('1.txt','utf8',(err,result)=> {
            resolve(result);
        });
    });
}
function p2(){
    return new Promise((resolve,reject)=>{
        fs.readFile('2.txt','utf8',(err,result)=> {
            resolve(result);
        });
    });
}
function p3(){
    return new Promise((resolve,reject)=>{
        fs.readFile('3.txt','utf8',(err,result)=> {
            resolve(result);
        });
    });
}
p1().then((r1)=>{
    console.log(r1);
    return p2();
}).then((r2)=>{
    console.log(r2);
    return p3();
}).then((r3)=>{
    console.log(r3);
})
